1. Technical Field
This invention relates generally to concrete; and more particularly to a method and apparatus for making an improved concrete using a non-chemical admix.
2. Description of Related Art
Concrete is known in the art as a hard strong building material made by mixing a cementing material and a mineral aggregate with sufficient water to cause the cement to set and bind the entire mass. Concrete has been in use since Roman times, and is made up of four main ingredients: coarse aggregate (gravel, usually between 0.5 to 1.5 inch in diameter), fine aggregate (sand, usually between 0.005 and 0.25 inch in diameter), cement (e.g., Portland cement), and water. Air also plays an important part, and often special additives (called admixtures or admixes) are also added to improve or modify the concrete's properties. Concrete is one of the most versatile construction materials available in the world.
Cement for making concrete is known in the art, and cement used in construction is characterized as hydraulic or non-hydraulic. Hydraulic cements (e.g., Portland cement) harden because of hydration, chemical reactions that occur independently of the mixture's water content; they can harden even underwater or when constantly exposed to wet weather. The chemical reaction that results when the anhydrous cement powder is mixed with water produces hydrates that are not water-soluble. In comparison, non-hydraulic cements (e.g., lime and gypsum plaster) must be kept dry in order to retain their strength. Portland cement is produced by pulverizing clinkers consisting essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter ground addition. Clinkers are nodules (diameters, 0.2-1.0 inch [5-25 mm]) of a sintered material that is produced when a raw mixture of predetermined composition is heated to high temperature. The low cost and widespread availability of the limestone, shales, and other naturally occurring materials make Portland cement one of the lowest-cost materials widely used over the last century throughout the world.
Admixtures for making concrete are known in the art and include materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. Admixtures made from powder or fluid are known in the art as “chemical” admixtures. In normal use, admixture dosages are less than 5% by mass of cement, and are added to the concrete at the time of batching/mixing. The common types of chemical admixtures are as follows: accelerators, retarders, air entrainments, plastercizers, pigment, corrosion inhibitors, bonding agents and pumping aids. The accelerators speed up the hydration (hardening) of the concrete. Typical materials used are CaCl2, Ca(NO3)2, and NaNO3. However, use of chlorides may cause corrosion in steel reinforcing and is prohibited in some countries and therefore nitrates may be favoured. The retarders slow the hydration of concrete, and are used in large or difficult pours where partial setting before the pour is complete is undesirable. Typical polyol retarders are sugar, sucrose, sodium gluconate, glucose, citric acid, and tartaric acid. The air entrainments add and entrain tiny air bubbles in the concrete, which will reduce damage during freeze thaw cycles thereby increasing the concrete's durability. However, entrained air is a trade-off with strength, as each 1% of air may result in up to a 5% decrease in compressive strength. The plastercizers increase the workability of plastic or “fresh” concrete, allowing it be placed more easily, with less consolidating effort. Typical plasticizers are lignosulfonate. Plasticizers can be used to reduce the water content of a concrete while maintaining workability, and are sometimes called water-reducers due to this use. Such treatment improves its strength and durability characteristics. Superplasticizers (also called high-range water-reducers) are a class of plasticizers that have fewer deleterious effects, and can be used to increase workability more than practical with traditional plasticizers. Compounds used as superplasticizers include sulfonated naphthalene formaldehyde condensate, sulfonated melamine formaldehyde condensate, acetone formaldehyde condensate, and polycarboxylate ethers. The pigment can be used to change the color of concrete, for aesthetics. The corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete. The bonding agents are used to create a bond between old and new concrete. The pumping aids improve pumpability, thicken the paste, and reduce separation and bleeding.
Consistent with that stated above, the durability of concrete is a strong function of the entrained air levels within the mix. Inadequate levels reduce the freeze thaw durability and too high of level reduces its strength. It is estimated that entrained air can typically reduce the strength of concrete by about 2-4% per 1% entrained air. The nominal levels of entrained air are in the 4% to 6% range. In order to achieve this, concrete manufacturers typically add admixes to control the air level. Generally, there is significant variation in the entrained air levels from mix to mix and tight control is difficult to maintain. It is also known in the art to add fishing line into the wet concrete mixture in order to improve the durability of concrete.
There is a need in the industry to control the air levels as well as improve the strength of aerated concrete.